1. Field of the Invention
The present invention relates to navigating to a predetermined position using positioning information from satellite navigational equipment or similar positioning technology.
2. Art Background
The art of surveying and mapping has dramatically changed through the use of satellite navigation equipment. Satellite survey devices include receivers that receive position signals from the global positioning system (GPS), Global Navigation Satellite System (GLONASS) receiver or other satellite or pseudolite systems. The position signals are used to compute the position of the receiver.
While selective availability (S/A) and environmental conditions may degrade the position signals to 100 meter accuracy, differential correction (DGPS) and real time kinematic (RTK) processes may be employed increase accuracy to the within 1 to 2 centimeter accuracy. RTK and real time computation of DGPS both require the use of an additional radio frequency receiver for reception of additional data that is used to compute a corrected, more accurate, position. Thus, the satellite survey device which is typically called the "rover device", includes a range pole for identifying the point for which a location is to be computed, a user input/output device for entry and display of information and data, a satellite receiver and a radio receiver.
A simplified drawing of a user employing prior art surveying equipment is shown in FIG. 1. The range pole 110 has attached to it an antenna 120 for receiving GPS signals and a circular level or vial 130. The user 140 holds the range pole 110 and moves the range pole 110 about until the level 130 indicates that the range pole 100 is vertically oriented and the bottom of the pole touches a location to be surveyed, such as location 150, 151 or 152. Once vertically oriented, the information received via the GPS antenna can be used to accurately compute the position of the location (150, 151 or 152). Typically, the user will have a backpack 160 that includes a wireless link, such as a radio modem 170, for receiving additional data, e.g., correction signals, from a reference station, e.g., a differential GPS (DGPS) base station. Using DGPS technology, more precise measurements are obtained. The backpack 160 also contains equipment and circuits for generating positional information based upon the signals received through antenna 120 and wireless link 170. The data collection device 100 enables the user to make manual entries, and also provides a visual reading of the survey measurements obtained.
Referring again to FIG. 1, a typical method of navigating to a known position will now be described. The user 140 navigates to a location of interest 152 by inputting the desired position in latitude and longitude (or any convenient x, y, z coordinate system) to the survey device and then following on screen directions such as an indication of the direction and distance from the user's current position. The on screen indications are useful while the user 140 is approaching the location of interest 152 from a distance; however, the on screen indication may change wildly when the user 140 is very close to the desired position. Therefore, once the user 140 is within a few meters, the user's pace must be slowed to assure the point 152 is not passed over. When the user 140 has identified an estimated location (150, 151, 152) that is believed to be the location of interest 152, the process of confirming the estimated location (150, 151, 152) may begin. This iterative process typically involves placing the range pole 110 over the estimated location (150, 151, 152), leveling the range pole 110, receiving a measurement, and adjusting the placement of the range pole 110. This confirmation process continues until the measurement received matches the position of the location of interest 152. In the example depicted, at t1, the user 140 initially estimated the desired location 152 to be at location 150. After receiving feedback from the input/output device, at t2, the user 140 adjusted the placement of the range pole 110 to location 151. Upon receiving the second measurement, the user 140 adjusted the placement of the range pole 110 to location 152 at t3. At this point, the user 140 received confirmation that the range pole 110 was in fact positioned over the desired location 152.
In light of the foregoing, it would be advantageous to eliminate the iterative and time consuming process of receiving a position measurement and adjusting the placement of the range pole until the desired location is found. Thus, it is desirable to provide an accurate survey device with an integrated pointing device for identifying the location of interest to the user from a distance.